It's a well-known fact with hydrodynamicists that roughness on a propeller reduces the efficiency: more torque needed to produce the same thrust. All scratches and gouges contribute to roughness, so it's better to have polished blades.

Of course it's not bunk for hydroplanes and racing boats that are polished before each heat of racing.. What you seem to forget is it's a real world. 3 days after you put your highly polished bronze prop in the salt water it will be rough again. Within a couple weeks it will have a small barnacle or two.. you get the picture....
Hell, by your theory we should all be polishing our boat bottoms and keeping them out of the water, unfortunately, as I say.. it's not practical. BTW, at some speeds bumps on your prop are better... which is why some Jet turbine blades actually are built with pebble size bumps on them....

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__________________"I spent most of my money on Booze, Broads and Boats. The rest I wasted" - Elmore Leonard

I wasn't forgetting the real world at all. I trust you didn't read the article I pointed to. Its authors observed that a polished substrate, in the real world, got only about 10% as many barnacles as the unpolished one. That seems like a win to me, so I'll keep polishing. I actually find it a pleasant way to while away a half-hour or so during the winter months, on a day when the weather's not good for iceboating here in New England. If I didn't have to haul my boat, I wouldn't haul just to be able to polish the prop, of course. But since it's out for 7 months anyhow, why not?

I dislike the idea of sanding the prop at each haulout. I use a plastic broadknife to scrape what I can and I've found that vinegar works very well to clean and brighten the prop and is dirt cheap. I mix it with flour to a sloppy peanut butter consistency and use that to coat the prop. Cover with an old plastic shopping bag to reduce drying and let soak for around 20 minutes or so. Scrub off with a scotch bright pad and repeat as required. Any remaining barnacle remnants can be easily dislodged afterwards with a flat blade screwdriver directly applied and a bump of the hand. Throw on a coat of lanolin grease and good to go.

I have read that if, when you come to a stop & anchor, you bag the prop with a plastic garbage bag, you will severely limit the growth. There is a convenient device with velcro for 'hiding' the prop. I wonder if you seed the bag with bleach or vinegar you might prevent & kill the buggers?

Of course it's not bunk for hydroplanes and racing boats that are polished before each heat of racing.. What you seem to forget is it's a real world. 3 days after you put your highly polished bronze prop in the salt water it will be rough again. Within a couple weeks it will have a small barnacle or two.. you get the picture.....

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How about a boat with an electric drive, left engaged at the dock with a solar panel hooked up. Just enough rpm to keep anything from being able to start growth...?

How about a boat with an electric drive, left engaged at the dock with a solar panel hooked up. Just enough rpm to keep anything from being able to start growth...?

Just hope that nobody gets their fishing line or other cordage in your prop. After a couple of weeks you could have sort of a problem LOL! Yeah I know, most marinas have rules against fishing but stuff happens. Where there are fish, somebody is gonna fish, at least until he gets caught.

Another potential problem is overrheating the motor. At low RPM the fan is doing bsically nothing at all. With the boat tied up at the pier, you have more load on the motor than if you were motoring free. I say potential because I just don't know for sure if all the factors add up to an overheting situation. Most newer motors have built in thermistors and most turnkey setups should have overheating protection, but it would be good to personally monitor your motor for a day or two. Also, realize that your solar only produces juice a few hours a day. I think your shore powerbatterycharger would be doing most of the work.

Nevertheless it is a fact that a turning prop will foul more slowly than a stationary one. What speed would be effective? I am GUESSING that you would want at least 100 prop RPM. Maybe 2 amps into the motor? 3 amps, maybe?

Sounds like a good experiment. Do you have electric drive? I am converting to electric (ME0907) when I get home.

I use a brass wire wheel in a drill. Takes less than 30 min, and leaves the prop shiny and smooth. I also have a folding prop. You do not need any type of chemical cleaners. Brass wire wheels can be purchased at any big box stores. Done.

It's a well-known fact with hydrodynamicists that roughness on a propeller reduces the efficiency: more torque needed to produce the same thrust. All scratches and gouges contribute to roughness, so it's better to have polished blades.

Alain

Polished is truly better as noted. The effectiveness is greater at higher power and rpm. I suspect it is hardly worth fretting over a great deal at 1000 to 1500 rpm and 6 knots. I think anything better than a 32 micro-finish will not be noticed. If there is hard data to show otherwise, I'd be glad to see it. Most of the anti-fouling coatings want you to clean & rough the surface and the resultant finish is pretty smooth after coating. Sailing the Great Lakes, we don't coat the prop anyway.

I use a brass wire wheel in a drill. Takes less than 30 min, and leaves the prop shiny and smooth. I also have a folding prop. You do not need any type of chemical cleaners. Brass wire wheels can be purchased at any big box stores. Done.

Me too, cup shaped wire wheel in an angle grinder. 2 minutes and the prop is smooth dull bronze again ready for the years coat of antifoul paint on top of a primer, seems to work well.